The present invention pertains to acoustic charge transport (ACT) devices and more particularly to an arrangement for reducing the effects of the clock signal level present at the input and output of an ACT device.
In ACT devices, a clock signal is used as a carrier to transport charge packets representing data through the semiconductor medium. The clock signals are greater in voltage than that manifested by the change representing the data themselves and therefore have a great effect on the ability of interface circuitry to recognize the data and not react to clock signals. Therefore, it is important to provide a notch filter on the ACT substrate which can remove the unwanted clock signals before downstream processing, without sacrifice of the broad signal bandwidth.
Notch filters which perform this function are typically built utilizing inductors. One such arrangement is shown in U.S. Pat. No. 4,577,168, issued to Clinton S. Hartmann on Mar. 18, 1986, and entitled "Notch Filter." The use of inductors creates a problem in that inductors are large in size, must typically mounted off the substrate of the ACT device and introduce a phase shift to the signals. U.S. Pat. No. 4,599,587, issued on July 8, 1986 to C. Hartmann et al. and entitled "Impedance Element" pertains to unidirectional SAW transducers for use in notch filters.
If inductors are put on the substrate with the ACT device, such inductors exhibit a low Q. Therefore these low Q circuits are not as useful as ACT chips with inductors which are not implemented on the substrate. In addition, inductors which are off the substrate have a sizable weight by comparison to the ACT device. The size of such inductors is large. Furthermore, separate inductors increase the part count, cost of assembly, and overall cost of the circuitry.
Accordingly, it is an object of the present invention to provide a notch filter for reducing the clock signal feedthrough effects in acoustic charge transport devices without the use of inductors.
It is a further object of the present invention to implement the notch filter monolithically with the acoustic charge transport device.